What does poison ivy look like, and how do I treat the rash it causes? —Sheri Lane, Lavigne, ON, Canada
The old line about poison ivy (“leaves of three, let it be”) is a useful way to remember what not to touch on your next foray into the overgrown patch at the back of the garden. The leaflets of poison ivy (Toxicodendron radicans) grow in groups of three; they’re yellow-green in spring, green in summer, and red to golden yellow in fall (in fact, in the mid-1700s, people bought pots of poison ivy for its lovely fall foliage).
Poison ivy is a perennial vine or shrub. It likes all types of soil, and tolerates full sun, full shade, and every condition in between.
If you’re gardening near poison ivy, wear clothing that covers your arms and legs, and wash the clothing as soon as you’re done. Urushiol, the oil in the plant, can remain on clothes, gloves, and shoes for months or years, and contact with it can cause just as much misery as direct contact with the plant.
If you do brush against poison ivy, here’s what to do: As soon as possible (ideally within 5 minutes), rinse with cool water. This may prevent the urushiol from binding to your skin. If it’s been longer than 30 minutes, relieve itching by taking a cool shower, soaking in an oatmeal or baking soda bath, and applying calamine lotion. If you have a severe case (or have had severe cases before), check with your doctor about medications to control the rash.
What’s the best way to get rid of poison ivy? —Susan Milinski, Berwick, ME
Poison ivy (Rhus radicans) is a woody perennial that loses its leaves and goes dormant each fall, then resumes growing in spring. If you don’t dig it out, you must spray the plant with weed killer while it’s actively growing. Once leaves start to show fall color, an abscission layer forms where leaves are attached to the stems. This causes leaves to drop and interferes with herbicide moving from the foliage to the roots.
Herbicides that are effective against poison ivy include glyphosate and triclopyr, available under several brand names. Look for products marked “woody-brush killer” or “poison-ivy killer.” Spray or wipe the herbicide directly on the poison ivy leaves, but don’t get any on desirable plants because it will harm them. Pick a day when the air is calm, temperatures range from the high 50s to low 80s, and no rain is forecast for at least 24 (preferably 48) hours. You may have to repeat the treatment a number of times if plants are large and well-established.
If you choose to dig up your poison ivy, bury it in an out-of-the-way location where it can disintegrate without anyone getting into it accidentally. Burning is unsafe because the fumes are dangerous when inhaled. Do not throw it in your compost pile, because it can be hard to tell when it’s completely broken down.